Various specialized medical devices, such as cardiac leads, ultrasonic catheters, balloon angioplasty catheters, ablation catheters, electrophysiological diagnostic catheters, pressure monitoring catheters etc., require the use of a delivery system for deploying the device in a desired internal body space, such as the heart or vascular system. Delivery systems can include an introducer and guide catheter, which are typically tubular, sheath-based systems. A guide catheter may be advanced to a desired internal body location, and a medical device deployed through a central lumen of the catheter.
Cardiac leads are often placed in contact with the cardiac tissue by passage through a venous access, such as the subclavian vein, the cephalic vein, or one of its tributaries, using an introducer and guide catheter. In such a manner, transvenous leads may advantageously be placed in contact with the heart without requiring major thoracic surgery. A multi-step procedure is generally required to introduce such leads within the venous system. Generally this procedure consists of inserting a hollow needle into a blood vessel, such as the subclavian vein. A wire guide is then passed through the needle into the interior portion of the vessel. The needle is then withdrawn and an introducer sheath is inserted over the wire guide into the vessel. The introducer is advanced into a suitable position within the vessel, i.e. so that the distal end is well within the vessel but the proximal end is outside the patient. Next the wire guide is removed. The introducer is left in position and therefore offers direct access through its hollow lumen from outside the patient to the interior of the blood vessel. For a description of these general procedures, reference is made to U.S. Pat. No. 5,713,867 issued to Morris, incorporated herein by reference in its entirety.
A guide catheter may be advanced through the venous access provided by the introducer to reach a monitoring or treatment site within the cardiovascular system. A cardiac lead, or other specialized medical device, may then be passed through the guide catheter to reach the desired location. Cardiac leads, which are highly flexible, are sometimes advanced over a guidewire or stylet that provides the lead with the stiffness needed to advance it through a venous pathway. This multi-step procedure can thus require several tools and requires considerable skill to perform.
After the lead is satisfactorily positioned, the guide catheter can be removed. One limitation of a sheath-based delivery system is that a sheath enclosing a lead generally cannot be removed over a standard cardiac lead connector assembly. Cardiac leads typically have a relatively bulky connector assembly that can be 1 to 3 times wider than the lead body at the proximal end. Therefore, cardiac leads are commonly introduced using a splittable or slittable introducer or guide catheter so that the sheath may be removed from around the lead by being slit apart. In such a manner the sheath does not have to be removed over the relatively bulky connector assembly at the proximal end of the lead. A slittable introducer sheath is disclosed in the above referenced U.S. Pat. No. 5,713,868. A slittable guiding introducer is described in U.S. Pat. No. 6,277,107 issued to Lurie et al. Slitting a guide catheter generally requires a slitting tool and can be a time-consuming task.
After being split apart and removed, a guide catheter cannot be reused and is discarded. Thus such split or slit guide catheters are normally single-use devices. A further limitation of using a slittable guide catheter, therefore, is that, if additional leads or devices need to be placed during the same surgical procedure, a new guide catheter is required. Furthermore, a situation sometimes arises that requires repositioning of an implanted cardiac lead. A lead may need to be repositioned, for example, when unacceptable thresholds for pacing or defibrillation are measured during an implant procedure or later after the lead has been chronically implanted.
Repositioning an implanted lead normally requires that the lead be removed from the patient's body and guided to a new implant site using the same multi-step process described above utilizing a new guide catheter. The proximal connector assembly on the implanted lead prevents an introducer or guide catheter from being inserted over the implanted lead to allow repositioning while the lead is still within the patient's body.
A further limitation of a sheath-based guide catheter is that the guide catheter can add a substantial increase to the overall diameter of the device as it is being delivered. Recent interest in pacing in the left heart chambers has led to the development of small diameter coronary sinus and cardiac vein leads. These leads are typically placed by advancing a guide catheter into the coronary sinus ostium, then advancing the lead into the coronary sinus and further into a cardiac vein as desired. Guide catheters may be too large in diameter to be advanced further than the coronary sinus or cardiac veins. Because a cardiac lead must be highly flexible in order to withstand the beating motion of the heart, a stylet or guidewire passed through a central lumen of the lead is often required in order to provide the lead with the stiffness needed to advance the lead further into the cardiac veins, without the support of the guide catheter. However, requiring a central lumen for a guidewire or stylet increases the size requirement of the lead. A guidewire or stylet may not provide effective torque transfer needed for fixing a lead by rotation.
Yet another limitation of sheath-based delivery systems is that the cardiac lead or other medical device being introduced may include sensors or electrodes along the body of the lead or device, which are enclosed within the guide catheter sheath. During the implant procedure, as long as the guide catheter is in place, these electrodes or sensors are not available for making measurements that may be of interest. For example, a cardiac defibrillation lead generally includes one or more defibrillation coils carried on the lead body. In order to verify that a lead position is acceptable, defibrillation thresholds are generally measured by inducing an arrhythmia after placing the lead and delivering defibrillation therapy through the defibrillation coil(s). A guide catheter sheath would need to be removed from the lead in order to perform these tests. If the defibrillation thresholds are unacceptable, the lead will need to be repositioned. If the guide catheter has already been removed, the lead must be removed and repositioned after placement of a new guide catheter.
Other types of sensors may be provided along the body of a lead or medical device, such as electrogram sensing electrodes, ultrasonic sensors, pressure sensors, etc. These sensors could be used for making measurements during an implant procedure to provide diagnostic or other information to and aid the physician in identifying and/or selecting an optimal implant site for the medical device.
To address some of these limitations, various non-sheath based delivery systems have been described. For example, U.S. Pat. No. 6,185,464 to Bonner et al. describes an arrangement for introducing and implanting an endocardial lead that includes pusher means for advancing a cardiac lead transvenously alongside a guide body. In this arrangement, a guide body tracking and cardiac lead engaging means includes a guide body tracking lumen that engages the guide body and a lead body receiving lumen that tightly grasps a lead body in a normal clamped state. By expanding the guide body tracking lumen, effected by an expandable balloon, the lead body receiving lumen is expanded to receive or release a lead body.
U.S. Pat. No. 6,129,749 issued to Bartig et al. discloses a pacing lead having a molded support body at its distal end, which supports an electrode and includes a lumen for a guidewire. This additional feature increases the size of the distal end of the lead. Additional features on the medical device itself are generally undesirable because these features may increase the cost or complexity of manufacturing the device. An additional feature for engaging a delivery device may not be a standard feature of many medical devices, limiting the utility of a delivery system requiring such a feature to only certain devices equipped with that additional feature.
Medical therapy or diagnostic devices may also need to be delivered to an internal body organ or space through an open surgical approach rather than a vascular approach. For example, in order to place an epicardial lead on the heart, a thoracotomy is generally required to approach the heart. Still some areas of the heart may be difficult to approach, even through a thoracotomy, requiring a larger incision or lifting or moving of the heart itself. A medical device delivery system that allows a device to be guided to an internal body location, such as the epicardial surface, through minimally sized incision can reduce the invasiveness and difficulty of the procedure.
Furthermore, a medical device may need to be inserted at a depth within the targeted tissue, requiring a small incision or stab wound into the tissue to place the medical device. A hollow, splittable needle is described in U.S. Pat. No. 5,443,492, issued to Stokes, for application of an active fixation lead into the epicardial heart tissue. The lead is carried in the lumen of the hollow needle to aid in inserting the distal end of the lead into the heart tissue but the needle is not used for guiding the lead to the implant site. In order to make the small incision or stab wound that may be required to place a medical device, a larger skin incision may sometimes be required to enlarge the open approach to the site to perform these procedures. A delivery system that allows a stab wound to be made without a fully open approach may reduce the invasiveness of such a procedure and allow a device to be more easily guided to and inserted into a desired tissue site.
It is desirable, therefore, to provide an improved non-sheath based medical device delivery system that allows electrodes, sensors, or other components mounted on a lead or catheter body to be exposed and operational during a surgical procedure. It is further desirable that such a system may be provided at a reduced size to allow delivery of small diameter cardiac leads or other devices into small diameter vessels. It is also desirable that a medical device delivery system be capable of guiding and, if necessary, inserting a medical device into a tissue site. A medical device delivery system should be easily mounted on or removed from the body of a medical device, without requiring complicated system components or special features on the medical device body. Moreover, it is desirable that the delivery system be removable from a medical device without slitting, splitting or otherwise rendering the device unusable for delivering multiple devices during a single surgical procedure or repositioning a device without first having to remove the device from the patient's body.